This invention relates to compositions comprising ternary alkyl sulfonium salts which are molten at low temperatures, and to the use of such compositions as electrolytes in electrochemical salts.
A class of molten compositions which is of special interest in the field of electrochemical cells is the class of fused salt compositions which are molten at low temperature and are useful as electrolytes. Such molten or fused salt compositions are mixtures of compounds which are liquid at temperatures below the individual melting points of the components. The mixtures can form molten compositions simultaneously upon contacting the components together or after heating and subsequent cooling.
Some of these molten or fused salt compositions are useful as electrolytes in batteries, photoelectrochemical cells, electrorefining and electroplating. Examples of low temperature molten fused salts are the chloroaluminate salts discussed by Wilkes, J. S., et al; in J. Inorg. Chem., Vol 21, 1263-1264, 1982. Alkyl imidazolium or pyridinium salts are mixed with aluminum trichloride (AlCl.sub.3) to form the fused chloroaluminate salts. Also chlorogallate salts made from gallium trichloride and methylethylimidazolium chloride are discussed in Wicelinski et al, "Low Temperature Chlorogallate Molten Salt Systems," J. Electrochemical Soc., Vol. 134, 262-263, 1987. The use of the fused salts of 1-alkylpyridinium chloride and aluminum trichloride as electrolytes is discussed in U.S. Pat. No. 4,122,245. Other patents which discuss the use of fused salts from aluminum trichloride and alkylimidazolium halides as electrolytes are U.S. Pat. Nos. 4,463,071; 4,463,072 and Great Britain Patent Application GB No. 2,150,740A. Unfortunately, the alkylimidazolium salts are difficult to prepare, and the alkyl pyridinium salts are too easily reduced in an electrochemical cell system.
Another class of fused salt compositions are the compositions formed from a metal halide and a hydrocarbyl-saturated onium salts containing at least one aromatic group, which are disclosed in U.S. patent application Ser. No. 046,010, now U.S. Pat. No. 4,764,440 which was allowed on Mar. 2, 1988. It would be desirable, however, to have fused salt compositions which exhibit higher conductivities than the fused salt compositions from those hydrocarbylsaturated aromatic-containing onium salts.
In view of the deficiencies of known compositions, other electrolyte compositions which have improved stability or conductivity are desired.